The invention relates to a solid electrolyte, to a process for its manufacture and also to devices comprising it.
Lithium microbatteries are used in small-size electronic devices and also in semiconductor devices.
The electrolyte is a component that has a strong influence on the electrical performance of these microbatteries.
This is because the failures observed during cycling are often linked to an electrochemical degradation of the electrolyte in contact with lithium.
The performances of microbatteries are closely linked to the electrical properties of the electrolyte, such as the ionic and electronic conductivity.
These microbatteries are used in chip cards, smart labels, and supplying power to real-time clocks and microsystems.
All these applications force all the layers necessary for the operation of the battery to be, on the one hand, solid and, on the other hand, manufactured with techniques that are compatible with the industrial processes of microelectronics.
Among the solid electrolytes, two families can be distinguished: polymers and glasses.
In solid polymer electrolytes, a lithium salt is directly dissolved in the polymer matrix. The ionic conductivity is commonly attributed to the mobility of the Li+ ions within the amorphous matrix of the solid polymer.
However, the solid polymer electrolytes have a low glass transition temperature, which generates the formation of crystalline zones capable of trapping the Li+ ions and of inhibiting their mobility.
Furthermore, the method of producing polymer electrolytes does not make it possible to produce depositions that conform to the substrates, that is to say having the same thickness at all points of the substrate.
It is for these two reasons that the electrolyte commonly used today for producing a microbattery is a glass.
The term “glass” is understood to mean an amorphous material.
Among the glass described in the prior art, only inorganic glass such as LiPON (Lithium Phosphorus OxyNitride), LiSON (Lithium Sulphur OxyNitride) or LiSiPON (Lithium Silicon Phosphorus OxyNitride) are used as electrolytes.
In this family, LiPON is the solid electrolyte most used in current microbatteries as it has a good electrochemical stability with respect to lithium. However, it has a relatively low ionic conductivity, of around 2×10−6 S/cm at ambient temperature, compared to that of certain polymer electrolytes.
Besides, organic glass such as amorphous carbon (a-CxHy) or PDMS-like materials (SiOxCyHz) are commonly used in microelectronics. But in this case, they are used as insulators at the interconnections and not as an electrolytic organic glass.